Combustion apparatus

ABSTRACT

The present invention provides a combustion apparatus capable of obtaining a smaller heating value than usual and capable of reducing the amount of a mixed gas without causing a change in the mixture ratio of air and a fuel gas. A shutter member  4  is provided, which narrows the flow passage of a gate section  25  of a duct  23  when a mixed gas, which is produced by mixing air and a fuel gas, is forcibly sent from the duct  23  to a distribution chamber  12  by a fan  2.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a combustion apparatus provided with a premixing device adapted to forcibly send a mixed gas, which is generated by mixing a fuel gas with air, to a gas burner.

Description of the Related Art

In general, a premixing device provided in a combustion apparatus is configured to mix air and a fuel gas at a predetermined ratio to generate a mixed gas and to forcibly send the mixed gas to a gas burner by a fan.

Hitherto, as a premixing device of this type, there has been known a premixing device in which a butterfly valve is provided in an air intake section on the upstream side of a fan, and a gas passage from which a fuel gas is jetted is connected on the downstream side of the butterfly valve to generate a mixed gas (refer to Japanese Patent Application Laid-Open No. 2014-215007).

The butterfly valve regulates the degree of closure of the air intake section so as to increase or decrease the air intake resistance, thereby increasing or decreasing the amount of passing air. The gas passage is provided with a flow control valve which increases or decreases the amount of a fuel gas flowing through the gas passage.

The butterfly valve and the flow control valve are interlocked with each other. The butterfly valve and the flow control valve simultaneously regulate the amount of air and the amount of the fuel gas.

The minimum number of revolutions of the fan at which a stable air volume can be obtained is set as a lower limit value. For this reason, the heating value of a gas burner reaches a minimum when the fan is rotating at the lower limit value of the number of revolutions.

Meanwhile, a gas burner can be operated such that a heating value that is smaller than the heating value corresponding to the lower limit value of the number of revolutions of the fan, can be obtained by using the butterfly valve and the flow control valve described above. More specifically, the butterfly valve which is normally in a fully opened state is actuated to narrow an air intake section on the upstream side of the fan, and the supply amount of the fuel gas is decreased by the flow control valve. This enables the gas burner to operate with a smaller heating value than usual by decreasing the amount of a mixed gas while running the fan at a number of revolutions that is higher than the lower limit value.

However in the conventional premixing device, the butterfly valve and the flow control valve regulate the amount of air and the amount of a fuel gas at different positions. Hence, the mixed gas generated when a gas burner is operated with a smaller heating value than usual exhibits an unstable ratio between air and a fuel gas, and may cause a combustion failure of the gas burner.

SUMMARY OF THE INVENTION

In view of the background described above, an object of the present invention is to provide a combustion apparatus capable of reducing the amount of a mixed gas without changing the mixture ratio between air and a fuel gas when operating a gas burner such that a smaller heating value than a heating value (amount) corresponding to a lower limit value of the number of revolutions of a fan can be obtained.

To this end, a combustion apparatus in accordance with the present invention includes: a gas burner; and a premixing device which forcibly sends a mixed gas generated by mixing a fuel gas with air to the gas burner, wherein the gas burner has a plurality of flame holes and a distribution chamber in which a mixed gas directed toward the flame holes is evenly distributed, and the premixing device has a fan, an air intake passage which takes in air drawn in by the fan, a fuel gas supply passage through which a fuel gas at an atmospheric pressure is supplied to the air intake passage, a mixed gas flow passage through which a mixed gas produced by mixing air and the fuel gas and sent out to a downstream by the fan, is introduced into the distribution chamber, and a flow passage reducing device which changes a flow passage area of the mixed gas flow passage in a reducing direction.

The flow passage reducing device is positioned between the fan and the distribution chamber, and changes the flow passage area of the mixed gas flow passage in the reducing direction. If the flow passage area of the mixed gas flow passage is reduced by the flow passage reducing device, then the amount of the mixed gas directed toward the distribution chamber decreases.

Meanwhile, on the upstream side of the fan, the pressure in the air intake passage turns into a negative pressure as the fan rotates. The pressure of the fuel gas in the fuel gas supply passage is the atmospheric pressure, so that the fuel gas is drawn into the air intake passage having the negative pressure, and the air and the fuel gas are merged and then directed toward the fan. Thus, air and the fuel gas in the amounts based on the negative pressure in the air intake passage are mixed, producing the mixed gas. Therefore, even when the number of revolutions of the fan changes and the negative pressure at an air intake port changes accordingly, both the amount of air drawn in and the amount of the fuel gas drawn in will change, so that the ratio between air and the fuel gas will remain unchanged.

Further, the mixed gas already produced at a predetermined mixture ratio is sent out to the downstream side of the fan, so that reducing the flow passage area of the mixed gas flow passage on the downstream side of the fan by the flow passage reducing device makes it possible to decrease the amount of the mixed gas without changing the mixture ratio of air and the fuel gas.

Thus, according to the present invention, when operating a gas burner such that a smaller heating value than the heating value corresponding to a lower limit value of the number of revolutions of a fan can be obtained, the amount of a mixed gas can be decreased without causing a change in the mixture ratio between air and a fuel gas.

Further, in the present invention, the flow passage reducing device includes a gate section shaped like a rectangular opening, through which the mixed gas in the mixed gas flow passage passes; and a shutter member shaped like a rectangular plate, which narrows the gate section in a direction across the mixed gas flow passage thereby to reduce the mixed gas flow passage.

The flow passage reducing device has the gate section and the shutter member. In the present invention, the mixed gas in the mixed gas flow passage passes through the gate section. The shutter member narrows the gate section in a direction across the mixed gas flow passage. At this time, the shutter member shaped like a rectangular plate narrows the gate section shaped like a rectangular opening from one side, thus making it possible to accurately reduce the flow passage area, as compared with a case where, for example, a gate section shaped like a round opening is narrowed by decreasing the diameter thereof.

More specifically, if a flow passage reducing device is used, in which the gate section thereof is shaped like a round opening and the shutter member thereof narrows the gate section by reducing the diameter, then the error of the flow passage area at opening and closing will be a square of the dimensional error of the diameter, resulting in significant variations in the flow passage area. In contrast, in the flow passage reducing device according to the present invention, the shutter member shaped like the rectangular plate narrows the gate section shaped like a rectangular opening, thus permitting an extremely small error in the flow passage area at the time of opening and closing.

Further, in the present invention, the distribution chamber has a partition member that divides a combustion range of the gas burner into two cells, wherein the flow passage reducing device is configured to guide the mixed gas in the mixed gas flow passage into one of the two cells of the distribution chamber in a case where the flow passage area of the mixed gas flow passage is reduced to a predetermined area.

If the supply amount of the mixed gas to the gas burner is decreased, then the speed of jetting of the mixed gas through the flame holes of the gas burner decreases below a limit value, and the flame may be extinguished by the gas burner.

According to the present invention, therefore, the mixed gas is guided into one of the two cells of the distribution chamber when the flow passage area of the mixed gas flow passage is reduced. This arrangement virtually reduces the number of the flame holes, thus making it possible to prevent a reduction in the speed of jetting of the mixed gas through the flame holes. Hence, even if the supply amount of the mixed gas is decreased, flames will not be extinguished by the gas burner, enabling satisfactory combustion to be maintained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory perspective view illustrating a combustion apparatus according to an embodiment of the present invention;

FIG. 2 is an explanatory side view of a fan;

FIG. 3 is an interior plan view illustrating the fan and a duct partially cut away; and

FIG. 4 is a diagram illustrating the relationship between the number of revolutions of the fan and the heating value of a gas burner.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention will be described with reference to the accompanying drawings. A combustion apparatus according to the present embodiment is incorporated in a water heater (not illustrated).

Referring to FIG. 1, the combustion apparatus has a gas burner 1, a fan 2, and a fuel gas supply pipe 3, which is a fuel gas supply passage. The fan 2 and the fuel gas supply pipe 3 constitute a premixing device according to the present invention.

The gas burner 1 is provided such that a plurality of flame holes (not illustrated) opens downward thereby to form flames on the bottom surface of the gas burner 1.

A heat exchanger 11 is connected to the bottom part of the gas burner 1. The heat exchanger 11 has therein a meandering water pipe and a fin (not illustrated). The gas burner 1 heats water passing through a water pipe of the heat exchanger 11.

A distribution chamber 12 is connected to the top part of the gas burner 1. The downstream end of a duct 23, which will be discussed hereinafter, is connected to one side of the distribution chamber 12. The distribution chamber 12 forms a space in communication with the flame holes of the gas burner 1. Further, the interior of the distribution chamber 12 is divided into two cells by a plate-like partition member 13, which rises to the top surface of the gas burner 1. In the present embodiment, the partition member 13 is provided at a position where the volumes of the two cells become equal.

The duct 23 corresponds to the mixed gas flow passage in the present invention, and is connected to the downstream side of the fan 2. The mixed gas forcibly sent from the fan 2 passes through the duct 23 to be supplied into the distribution chamber 12. As illustrated in FIG. 2, the duct 23 has a flow passage having a rectangular shape in a sectional view.

The fan 2 has a motor 21 and an air intake pipe 22, which is an air intake passage, as illustrated in FIG. 2. The air intake pipe 22 is connected to the upstream side of the fan 2, and the lower end thereof is opened as an intake port. Connected to the air intake pipe 22 is the downstream end of the fuel gas supply pipe 3.

The fan 2 is a so-called turbine type, and provided with a rotatable turbine 24, as illustrated in FIG. 3. The turbine 24 is rotatively driven by the motor 21 (refer to FIG. 1 or FIG. 2).

The fuel gas supply pipe 3 is provided with a pressure regulation device 31 referred to as Zero Governor. The pressure regulation device 31 decreases the pressure of a fuel gas, which is supplied at a predetermined positive pressure, to the atmospheric pressure. In other words, the fuel gas flowing in the fuel gas supply pipe 3 passes through the pressure regulation device 31 so as to be supplied to the air intake pipe 22 at the atmospheric pressure.

When the turbine 24 is rotated by the motor 21 in the fan 2, a negative pressure is generated in the air intake pipe 22. This causes external air to be drawn toward the fan 2 through the air intake pipe 22. Further, since the downstream end of the fuel gas supply pipe 3 is connected to the air intake pipe 22, the fuel gas, the pressure of which has been decreased to the atmospheric pressure by the pressure regulation device 31, is drawn into the air intake pipe 22.

Thus, in the state in which the fan 2 is at a halt and no negative pressure has been generated in the air intake pipe 22, no fuel gas flows into the air intake pipe 22 from the fuel gas supply pipe 3. Once the fan 2 is actuated and a negative pressure is produced in the air intake pipe 22, the fuel gas at a flow rate which is proportional to the magnitude of the negative pressure will be drawn into the air intake pipe 22 from the fuel gas supply pipe 3.

Then, the fuel gas drawn into the air intake pipe 22 is mixed, in the fan 2, with air drawn in through the lower end of the air intake pipe 22, and supplied through the duct 23 to the gas burner 1.

The number of revolutions of the fan 2 corresponds with the number of revolutions of the motor 21. The magnitude of the negative pressure in the air intake pipe 22 increases or decreases according to the level of the number of revolutions of the fan 2. At this time, even if the magnitude of the negative pressure in the air intake pipe 22 increases or decreases, causing the amount of air drawn into the air intake pipe 22 to increase or decrease, the amount of the fuel gas drawn into the air intake pipe 22 from the fuel gas supply pipe 3 also increases or decreases accordingly at the same degree, so that the mixture ratio of the mixed gas supplied to the gas burner 1 will remain constant.

Further, in the present embodiment, the downstream end of the duct 23 is provided with a gate section 25 shaped like a rectangular opening, as illustrated in FIG. 3. Further, a shutter member 4, which is swingably supported, is provided inside the duct 23. The shutter member 4 is provided such that the rectangular plate part thereof closes half the gate section 25. The gate section 25 and the shutter member 4 constitute the flow passage reducing device in the present invention.

If the shutter member 4 fully opens the gate section 25, then the mixed gas from the duct 23 flows in the directions indicated by arrows A and B into both of the two cells partitioned by the partition member 13 in the distribution chamber 12. Meanwhile, if the shutter member 4 is swung to close half the gate section 25, then the mixed gas will flow only in the direction indicated by arrow B and flow into one of the two cells partitioned by the partition member 13.

If the shutter member 4 is fully opened, then flames will be formed in an area “a” corresponding to the entire surface of the gas burner 1. If the half of the gate section 25 is closed by the shutter member 4, then the flames formed will be concentrated mainly in an area “b.” Thus, even if the supply amount of the mixed gas decreases when the shutter member 4 closes half the gate section 25, an adequate amount of the mixed gas will be supplied to the flame holes, enabling the gas burner 1 to maintain satisfactory combustion.

Further, the flow resistance of the mixed gas flowing from the duct 23 toward the distribution chamber 12 is low when the shutter member 4 is fully opened, whereas the flow resistance of the mixed gas flowing from the duct 23 toward the distribution chamber 12 increases when the shutter member 4 closes half the gate section 25.

As the flow resistance of the mixed gas flowing from the duct 23 toward the distribution chamber 12 increases when half the gate section 25 is closed, the flow rate of the mixed gas will decrease even if the number of revolutions of the fan 2 remains the same, as compared with the case where the gate section 25 is fully opened.

As described above, the amount of the mixed gas is regulated by changing the opening degree of the gate section 25 by the shutter member 4, so that even if the flow rate of the mixed gas passing through the gate section 25 decreases, the mixture ratio of air and the fuel gas in the mixed gas will not be influenced, thus maintaining a constant mixture ratio.

Further, the gas burner 1 can be stably operated with a heating value which is smaller than a normal heating value corresponding to the number of revolutions of the fan 2 which is below a lower limit value, without causing the actual number of revolutions of the fan 2 to become smaller than the lower limit value.

The relationship between the number of revolutions of the fan 2 and the heating value of the gas burner 1 according to the present embodiment will now be described with reference to FIG. 4.

In FIG. 4, a straight line L1 indicates the relationship between the number of revolutions of the fan 2 and the heating value (input) of the gas burner 1 when the gate section 25 is fully opened. The number of revolutions of the fan 2 is proportional to the supply amount of the mixed gas. Hence, the heating value of the gas burner 1 is proportional to the supply amount of the mixed gas.

To decrease the heating value in the gas burner 1, the number of revolutions of the fan 2 is decreased. However, a lower limit value RL is set for the number of revolutions of the fan 2, so that the fan 2 cannot be rotated at a speed that is lower than the lower limit value RL. For this reason, if the gate section 25 is fully opened, then the lower limit value of the heating value will be CL1, and no heating value below CL1 can be obtained.

To further decrease the heating value, therefore, the gate section 25 is half closed by the shutter member 4. This causes the number of revolutions of the fan 2 and the heating value to have a correlation denoted by a straight line L2. Thus, decreasing the number of revolutions of the fan 2 to the lower limit value RL enables the heating value to decrease to CL2.

It is to be understood that the present invention is not limited to the disclosed embodiments, and various changes and modifications can be made within the concept and scope of the present invention. 

What is claimed is:
 1. A combustion apparatus comprising: a gas burner; and a premixing device which forcibly sends a mixed gas generated by mixing a fuel gas with air to the gas burner, wherein the gas burner includes a plurality of flame holes and a distribution chamber in which a mixed gas directed toward the flame holes is evenly distributed, and the premixing device includes; a fan; an air intake passage which takes in air drawn in by the fan; a fuel gas supply passage through which a fuel gas at an atmospheric pressure is supplied to the air intake passage; a mixed gas flow passage through which a mixed gas produced by mixing air and the fuel gas and sent out by the fan to a downstream, is introduced into the distribution chamber; and a flow passage reducing device which changes a flow passage area of the mixed gas flow passage in a reducing direction.
 2. The combustion apparatus according to claim 1, wherein the flow passage reducing device includes a gate section shaped like a rectangular opening, through which the mixed gas in the mixed gas flow passage passes; and a shutter member shaped like a rectangular plate, which narrows the gate section in a direction across the mixed gas flow passage thereby to reduce the mixed gas flow passage.
 3. The combustion apparatus according to claim 1, wherein the distribution chamber includes a partition member that partitions a combustion range of the gas burner into two cells, and the flow passage reducing device is configured to guide the mixed gas in the mixed gas flow passage into one of the two cells of the distribution chamber in a case where the flow passage area of the mixed gas flow passage is reduced to a predetermined area. 